1. Field of the Invention
The present invention relates to a stringed instrument, e.g., a guitar or a piano, and more particularly to a stringed instrument having a device that drives the strings thereof to sustain the vibration of the string and an electromagnetic driver for the device.
A guitar or a piano differs from a violin in that after the string of a guitar or a piano is excited, the magnitude of the vibration of the string will become half within about a half second and die within about 7 seconds. Particularly, for example, in the case of an electric guitar, it seems that the attenuation speed of the vibration of the string is shorter than that of an acoustic guitar because of the electric characteristics of an amplifier. Thus, an effector, which is a device for adding several sound effects, e.g., Delay, Reverb, Compressor, Overdrive, etc., to the sound of the guitar is often used to enable more sustained sound to be heard acoustically.
An effector using Delay or Reverb adds reverberations to a musical sound, and the sound is produced by recording and playing back the sound on a magnetic tape or by delaying the tone by a spring arrangement. Recently, simple electronic devices using BBD (Bucket Brigade Device) have been utilized for the Delay or the Reverb. An effector using a Compressor increases the amplitude of a music signal sent to by an amplifier in reverse proportion to attenuation characteristics of the vibration of the strings, and an Overdrive amplifies the signal beyond a generally permissible level so as to obtain a long tone. A longer tone can be achieved by using these effectors, although the effectors cannot maintain the tone after the vibration of the string has stopped.
Currently, musicians investigate various sounds and develop the art of musical performance in order to play said various sounds in response to their individual performance. For example, a style using a loudspeaker feedback is one that produces the sound of a guitar at high volume so as to sustain the vibration of the string on the guitar for a long time without attenuation by way of sympathetic vibration in cooperation with air vibration emitted from the loudspeaker. As described above, the feedback can maintain the vibration of the string for a long time, but in order to sustain the sound, the player must utilize a skilled and high-grade technique to overcome several limitations, i.e., sound volume, location of the amplifier, length of the strings and musical interval, etc. Further, there is a weak point in that the tone of the first string on the treble side, which is the most significant for musical expression, cannot be easily sustained. Therefore, a device that easily sustains the vibration of the string for an extended period has been in demand for a long time.
2. Description of the Prior Art
Several devices for sustaining the vibration of strings are disclosed in relation to an electric guitar. For example, U. S. Pat. No. 4,941,388 (Hoover, et al.) and U. S. Pat. No. 4,907,483 (Rose, et al.) disclose an arrangement of an electric guitar having such a device, the former is referred to by the trade name of "Sustaniac" and the latter by the trade name of "Kramer-Floyd Rose Sustainer" and both has been put into practical use and are available on the market.
Although an electric guitar having the device that is put into practical use as described above can excite and sustain the vibration of the strings quite adequately, there are some problems from the point of view of a musical instrument.
The first problem is that a stringed instrument, e.g., a guitar and a piano, has plural strings and the thickness and tension of every string is different, and so the driving force applied to each of them is also different. Namely, in a conventional case an electromagnetic driver of a stringed instrument having a device for sustaining the vibration of the string, for example an electric guitar, emits a constant driving magnetic energy against every string uniformly so that the first string that has the smallest mass and thickness and relatively large tension cannot be excited, oppositely, the fifth string and the sixth string can be excited easily because of the large mass and thickness and relatively low tension of the string.
Therefore, in such a self excitation system there are several defects in that a player cannot participate in the operation of volume control between the strings overall and various tones produced by large and small vibrations of each string give the player an unpleasant feeling occasionally, and although the first string is the most important for musical expression, the first string cannot be excited easily in comparison with the other strings since the first string is the finest out of the strings and its mass is the lightest.
Furthermore, there is another problem that a string other than the first string, e.g., the fifth string or the sixth string, experiences sudden self-excitation when providing the first string with increased driving force in order to solve the problem as described above.
It is difficult to maintain a balance between the vibration of each string as described above, and if an optimum magnetic energy output for driving a string is adjusted to the least excitable string, e.g., a first string, the optimum magnetic energy output for driving the first string provides a relatively excitable string, e.g., a fifth string or a sixth string, with excessive driving energy, and thereby, there is a problem in that a fifth string or a sixth string experiences sudden self-excitation by the excessive driving energy described above although the fifth or sixth string is not used for playing music. To prevent said problem, a musician must always mute the fifth and sixth string while playing the guitar and that is a serious problem for the musician.
Also, a method of playing a chord that simultaneously plays plural strings in such a stringed instrument is very important for musical performance, however, there is a defect in that only a particular string is excited by an excitation imbalance between the strings as described above and so it is impossible to play a chord in the prior art.
Next, the second problem is the emission efficiency of driving magnetic energy. Namely, for example in the case of an electric guitar, it is most preferable to mount a device for sustaining the vibration of a string on a guitar body as a package, and it is clear that an external effector type guitar is substantially inferior to an internal effector type guitar. Also in the internal effector type guitar, a power supply unit for a device for sustaining the vibration of a string must be essentially small, e.g., a small dry cell battery, to be mounted inside a guitar body. A driving current used to excite a string in such an excitation system is usually about 50 mA, and so the emission efficiency of driving magnetic energy is very important so as to prevent the necessity of frequently changing the dry cell battery.
As for an electromagnetic driver of a device for sustaining the vibration of a string mounted on an electric guitar, a bar type pole piece is generally used to enable the guitar to be played using a method for changing pitch, e.g., bending, in which a string is drawn on a fret parallel with the fret by the finger, and thereby, tension of the string and pitch vary. Conversely, a single type pole piece is scarcely used, because magnetic energy emitted from each pole piece corresponding to each string lies in the neighborhood of just above each pole piece so that a cut tone is generated if a string is out of the magnetic energy area while playing using the Bending method.
A bar type pole piece has a flat magnetic flux emitting characteristic and a magnetic field is formed in the up and down direction uniformly. However, circular magnetic fields are formed in the neighborhood of both side ends of a bar type pole piece. Therefore, a magnetic field provided to the strings from a second string to a fifth string is relatively stable and uniform, but a magnetic field provided to a first string and a sixth string is curved as described above so that magnetic field density falls and the driving force for driving a first string and a second string is smaller rather than that for other strings, and excitation balance between strings is lost thereby.
Further, magnetic flux emitted from a bar type pole piece in the reverse direction of the strings is not used to drive a string and so energy is wasted.